AVR-Chat

You might want to go back and add diodes across those solenoids, Owen.  
Transients on the power line can cause you all sorts of problems that a 
3 cent diode will solve.

We once had a customer who had us modifying some control modules that 
they sent all over the world.  They had a problem with something letting 
all the smoke out of the power drivers and warranty repairs were killing 
us.  I went over to their place and did some system evaluation and found 
the problem to be coming from transients generated by a clutch/brake 
assembly.  With a high voltage scope probe and Tektronix 465 scope, all 
I could see of the transient was about 1,000 volts...and it was way off 
the display so I never could see what the peak values were.  These 
transients were also several microseconds in duration.  A 1N4004 across 
the coil of the clutch/brake cured the problem...and we made money from 
then on.

The clutch/brake was drawing less than half an amp at 24 volts DC so it 
doesn't take a lot of current or voltage to generate humongous 
transients.  All it takes is a lot of ampere turns.  Diodes should be 
physically mounted as close to the solenoids as possible.


REB



OWEN-A wrote:

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>>I am trying to modifying a PIC program to get a shift register to work
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>>properly, toggle the clear pin on the shift register to force all outputs 
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>>to
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>>"0" to prevent it from holding the data for too long and burning out an
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>>expensive solenoid.
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>>The shift register is a 74HC595 and will occasionally lock an output on 
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>>for
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>>a long enough period to destroy a solenoid.
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>>These solenoids are $350-00 each and they burn out around 40 to 50 a year 
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>>on
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>>the system.
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>>Have tried a PIC group but have not received any replies.
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>>I normally use AVR's with a C compiler the more that I see of the PIC the
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>>more I dislike them!
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>Sounds like a problem with a transient on the supply. Something like an AVX 
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>TransGuard will cure the problem.
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>Leon 
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>These units are in the field on 12 volt battery supply with solar panel
>charging system (no mains supply) the 12 volt solenoid's are driven by
>VNP5N07 Fully protected power mosfets     (ST Microelectronics devices)
>switching one end of the solenoid to V- the other end of the solenoid is
>connected the battery V+ .
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>The 1N4004 protection diodes are across the mosfets "not the solenoids" (no
>diodes across the solenoids).
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>I had not noticed this before but perhaps the internal resistance of the
>batteries may be high enough that the ringing of the solenoid coil could be
>causing a spike on the supply??? 
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>Sorry for the HTML!
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>Thanking You,
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>Owen.
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>Yahoo! Groups Links
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